Thyroid Gland Anatomy Pharm-D

1. Arzoo Baltistani

3.  The thyroid gland weighs 10 to 20 grams in
normal adults.
 Thyroid volume measured by ultrasonography
(US) is slightly greater in men than women
 it increases with age and body weight.
 it decreases with increasing iodine intake.
 The thyroid is one of the most vascular organs in
the body. Thus, US measurements of thyroid
volume and even nodule size can differ markedly
from the size after devascularization and
resection.

5. The normal thyroid gland is immediately caudal to
the larynx and encircles the anterolateral portion
of the trachea.
The thyroid is bordered by the trachea and
esophagus medially and the carotid sheath
laterally.
The sternocleidomastoid muscle and the three
strap muscles (sternohyoid, sternothyroid, and
the superior belly of the omohyoid) border the
thyroid gland anteriorly and laterally

6.  It consists of two lobes connected by a narrow
isthmus.
 Each lobe is pyramidal in shape, with its apex
directed upward and its base directed
downward.
 The isthmus is the narrow part of the gland
connecting the two lobes.
 A small pyramidal lobe projecting upward
from the isthmus is often present to the left of
the midline.

8. The arterial blood supply to the thyroid gland is
primarily from the right and left superior and
inferior thyroid arteries, derived from the
external carotid arteries and thyrocervical
trunk, respectively.
The venous drainage consists of the superior,
middle, and inferior thyroid veins that drain
into the internal jugular vein and innominate
vein

9.  Superior thyroid artery is the first branch off the
external carotid artery. It extends inferiorly to the
superior pole of the thyroid lobe.
 In addition to supplying the thyroid, the superior
thyroid artery is the primary blood supply to
approximately 15 percent of superior parathyroid
glands.
 The superior thyroid artery is a landmark for
identification of the superior laryngeal nerve,
which courses with the artery until approximately
1 cm from the superior thyroid pole

10.  Inferior thyroid artery is a branch of the thyrocervical
trunk which arises from the subclavian artery.
 The inferior thyroid artery courses posterior to the carotid
artery to enter the lateral thyroid. The point of entry can
extend from superior to inferior thyroid poles.
 The inferior thyroid artery also supplies the inferior
parathyroid glands and approximately 85 percent of
superior parathyroid glands.
 The RLN may course anterior or posterior to the inferior
thyroid artery. In some cases, the RLN may branch into both
an anterior and posterior position.

11.  Thyroidea ima artery is found in approximately 3
percent of individuals and arises from the aortic
arch or innominate artery and courses to the
inferior portion of the isthmus or inferior thyroid
poles.
 Surgical control of the thyroidea ima artery is
essential during thyroidectomy.
 The thyroidea ima artery can be quite enlarged in
patients with thyroid disease such as goiter or
hyperthyroidism

12. Venous drainage
Superior thyroid vein:
 It arises from the upper part of the lobe.
 It ends into the internal jugular vein.
Middle thyroid vein:
 It arises from the middle of the lobe.
 It ends into the internal jugular vein.
Inferior thyroid veins:
 Arise from the isthmus and lower parts of the lobes.
 Descend in front of the trachea.
 End into the left brachiocephalic vein.

13. The lymphatic vessels of the thyroid gland drain into:
1) Pretracheal lymph nodes.
2) Paratracheal lymph nodes.
- The efferent of these nodes drain into
the deep cervical lymph nodes.

14. Thyroid Physiology
Synthesis of the thyroid hormone
Trapping of inorganic iodide from the blood
Oxidation of iodide to iodine.
Binding of iodine with tyrosine to form
iodotyrosines.
Coupling of mono-iodotyrosines and di-
iodotyrosine to form T3, T4

15. Synthesis of the thyroid hormone
The metabolic effects of the thyroid hormones
are due to unbound T4 and T3.
T3 is the more important and is also produced
in the periphery by conversion from T4.
T3 is quick acting (within a few hours)
whereasT4 acts more slowly (4-14 days)

17. Thyrotropin-releasing hormone (TRH) increases the
secretion of thyrotropin (TSH), which stimulates the
synthesis and secretion of trioiodothyronine (T3) and
thyroxine (T4) by the thyroid gland.
T3 and T4 inhibit the secretion of TSH, both directly and
indirectly by suppressing the release of TRH.
 T4 is converted to T3 in the liver and many other tissues
by the action of T4 monodeiodinases.
Some T4 and T3 is conjugated with glucuronide and
sulfate in the liver, excreted in the bile, and partially
hydrolyzed in the intestine.
Some T4 and T3 formed in the intestine may be
reabsorbed.
Drug interactions may occur at any of these sites.

18.  Fetal brain and skeletal maturation
 Increase in basal metabolic rate
 Increases sensitivity to catecholamines
 Stimulates gut motility
 Increase bone turnover
 Increase in serum glucose, decrease in serum
cholesterol

20.  Normal parathyroid glands are approximately the size of a
grain of rice or a lentil.
 Normal glands are usually about 5 by 4 by 2 millimeters in
size and weigh 35 to 50 milligrams.
Enlarged parathyroid glands can be 50 milligrams to 20
grams in weight, most typically weighing about 1 gram and 1
centimeter in size

21. Normal superior parathyroid glands are usually located
on the posterior-lateral surface of the middle to superior
thyroid lobe.
They lie under the thyroid superficial fascia, posterior to
the recurrent laryngeal nerve and can be visualized by
carefully dissecting the thyroid capsule in this region.

22.  The two inferior parathyroid glands reside in the anterior
mediastinal compartment, anterior to the recurrent laryngeal
nerve.
They are most often found in the thyrothymic tract, or just
inside the thyroid capsule on the inferior portion of the
thyroid lobes

23. The superior parathyroid glands receive most of their blood
supply from the inferior thyroid artery and also are supplied
by branches of the superior thyroid artery in 15 to 20 percent
of patients.
The inferior parathyroid glands receive their end-arterial blood
supply from the inferior thyroid artery.